The Influence of High Physical Demand on the Occurrence of Major Muscle and Ligament Injuries in Professional Soccer Athletes: A Systematic Review

Objective  The present systematic review aimed to investigate the influence of high physical demand on the increase in muscle and ligament injuries in professional soccer athletes. Methods  We analyzed scientific publications to determine the incidences of the main injuries, their causes and mechanisms, and their association with high physical demand. We compared amateur and professional players and assessed the effectiveness of FIFA11+ as a prevention alternative. Searches occurred on Scielo, Pubmed, and Google Scholar databases. The filters were the topic, publication date (last 5 years), and study relevance. The indexing terms were the following: Overuse , Calendar , Injuries , Muscular , Ligament , Athletes , Soccer , Football . We described the main data obtained to compare and analyze the results. This study complied with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement guidelines. Results  The query resulted in 24 articles published from 2019 to 2023. The high physical demand increased the risk of injuries. Most injuries occurred in the lower limbs. The most common injuries were strains, sprains, contractures, and ligament ruptures. FIFA11+ presented itself as a viable prevention alternative. Conclusion  We concluded that high physical demand increases the most frequent muscle and ligament injuries in professional soccer players, that is, strains, sprains, contractures, and ligament rupture, suggesting the FIFA11+ program as a prevention alternative.


Introduction
Soccer is one of the most popular sports worldwide.It is played in several countries by individuals from all age groups and both genders.However, professional soccer players present a high incidence of injuries due to the intense physical demand in training and matches throughout the year. 1,2he incidence of sports injuries and their risk factors is a subject of intense debate.The search for good performance and success in sports causes many players to undergo threshold physical effort or beyond their physiological limits, resulting in overload-related injuries. 3Soccer requires a lot of impact from physical contact, short, fast, and discontinuous movements such as acceleration and deceleration, jumps, and sudden directional changes. 1,4t is estimated that soccer accounts for 50 to 60% of sports injuries affecting different muscle groups, mainly in the lower limbs. 2Injuries often negatively impact not only the player's quality of life but the team's performance, resulting in strategic and economic losses to the club due to the absence in training and matches. 5aking care of the athlete's health and implementing injury prevention strategies are critical to maximize the team's chance of success and the player's professional growth.Therefore, knowledge of injuries emerges as a strategy for developing plans to prevent or minimize them in sports, reducing the losses and unhappiness resulting from players' absence. 6,7he growth of national and international competitions, especially with the increase in the number of official matches, makes it critical to know about the different types of injuries that affect soccer players the most with the goal of prophylaxis as well as taking care of the athlete's health and safety. 6Therefore, this study aimed to investigate and address the influence of high physical demand on the incidence of the main muscle and ligament injuries in professional soccer players.

Materials and Methods
We conducted this study according to the guidelines for systematic reviews, whose goal is to examine and discuss articles published on a determined topic. 8The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed.
The present study is a systematic review.The review had six stages: 1) identification of the topic and selection of the research question; 2) establishment of criteria for literature search and study inclusion and exclusion; 3) definition of the information to be extracted from the selected studies; 4) study categorization; 5) evaluation of studies included in the integrative review and their interpretation; and 6) review presentation.

► atletas ► futebol/lesões ► músculo esquelético ► traumatismos do joelho
The first stage used the Patient, Intervention, Comparison, and Outcome (PICO) strategy to define the following research question: "Does high physical demand have an influence in the increase of major muscle and ligament injuries occurrence in professional soccer players?"In this question, P refers to professional soccer players, I is high physical demand, C is regular physical demand, and O refers to increased occurrence.
We searched for articles about the intended outcome to answer this question using the terminologies registered in the Health Sciences Descriptors (DeCS) created by the Virtual Health Library and developed by the Medical Subject Headings of the U.S. National Library of Medicine, allowing the use of common terminology in Portuguese, English, and Spanish.The descriptors included Overuse, Calendar, Injuries, Ligament, Muscular, Athletes, Football, and Soccer.Keyword crossing used the Boolean operators and, or, and not.
The bibliographic survey occurred through electronic searches in the following databases: Scientific Electronic Library Online (SciELO), National Library of Medicine (PubMed), and Google Scholar.
The search took place in September 2023.For inclusion criteria, there was no language limitation, considering articles in English and Portuguese published in the last 5 years (from 2019-2023) about the topic and available electronically in its full format.Articles that did not meet the inclusion criteria were excluded.

Results
We identified a total of 315 studies.The time interval filter (2019-2023) application resulted in 157 articles for further investigation, according to the established exclusion criteria, generating a sample of 54 publications for complete reading.Of these 54 studies, we excluded 30 because they were irrelevant to the present study.The final sample for this review consisted of 24 articles.The flowchart (►Fig.1) demonstrates this paper selection process.
We tabulated the selected studies (►Table 1) 5,6,8-29 including authors' names and year of publication, type of article, title, study objective, and main findings.
Of the 24 articles selected, 16 were systematic reviews, 3 were field research, 3 were prospective studies, 1 was a systematic review and meta-analysis, and 1 was a clinical trial.However, they all address the main theme: the occurrence of sports injuries in soccer players.The authors' main objectives included investigating the prevalence of different types of injuries (looking for the most common ones), the different incidences of injuries in amateur (base categories) and professional players, the effectiveness of the FIFA11þ program as a preventive alternative and understanding the influence of risk factors and mechanisms for the occurrence of certain types of injury.

Functional Capacity
The functional capacity of the player is paramount because of the significant difference between professional and amateur athletes.Each age group requires different training strategies, with distinct loads, intensity of physical activity, exercise duration, and appropriate selection for each category.
The stratification of the sport modality and the variables from each athlete provide indications, such as ball techniques  Compared to other age groups, sub-16 and sub-18 players had higher incidence rates of overuse injuries.
In the remaining players, bruises, sprains, and growth-related injuries were the most common.Meniscus/cartilage injuries were the most severe lesions.
24 Aiello et al., 29 2022 Systematic review Injury-inciting activities in male and female football players: a systematic review High-intensity running and kicking activities may be the main triggers for thigh and groin injuries, while contacts may be the most common triggers for ankle injuries.Contact and pressure may be the most common inciting activities leading to anterior cruciate ligament injuries, but there is no consensus in the literature.
and game tactics, for players aged 8 to 11 years old, and individual preparation with an emphasis on movement speed, resistance, agility, and flexibility for players aged 12 to 17.This stratification highlights the role of grading intensity as age advances to preserve the athlete's physical health up to the professional level.Otherwise, the lack of planning, with exaggerated demands, may expose these players to greater chances of injuries. 21

Comparison of Amateur and Professional Players
Analyzing the incidence rate of injuries in high-level youth soccer, we noted an influence of advancing age, as older athletes have higher incidence rates.Among these injuries, 20% are severe, and result in absence for at least 28 days. 22his analysis is consistent with the fact that professional match calendars are more competitive and require greater physical demand compared with base (amateur) athletes.The higher frequency of short breaks between official matches, training intensity, time zone variation affecting rest, and the distinct climates from different locations, among other details, generate a set of factors contributing to higher physical wear and tear in professional players.
Younger athletes from base categories have a less intense calendar, with greater chances of preventing overload-related muscle and ligament injuries, partially explaining the different injury incidences.However, when comparing younger players from sub-9 and sub-19 categories, the latter presented high injury incidence rates due to the increasing training intensity and frequency of championship matches.Therefore, we infer that the higher intensity and match frequency, with no proper physical preparation, are risk factors for injuries even in young athletes. 28urthermore, this data demonstrates that the transition from amateur (base categories) to professional category, following the same notion of advancing age, could be a risk factor for the higher incidence rate in these athletes.

Training and Matches
The high physical demand for high-performance athletes increases the chance of injuries, more so in matches than in training sessions.Meanwhile, younger (amateur) players presented a higher incidence of injuries in training than in official matches. 23Moreover, groups with an age range closer to the professional category suffered more injuries than the others.For instance, a sub-20 player group had injury rates similar to professional players, especially in matches than in training, while the sub-17 group had a higher injury rate during training. 24This relationship is justified by the higher number of matches in the calendars of older age groups, which also happens in the transition from youth categories to professional soccer.
This information demonstrates that the load evolution during the athlete's progress to the professional category, if not balanced, has a strong relationship with the occurrence of injuries caused by the high physical demand in their training routine and matches.

Main Injuries
Injuries in soccer players, whether amateurs or professionals, mainly occur in the lower limbs.A study with male athletes competing in a regional soccer tournament investigated the incidence and prevalence of injuries and found that the lower limbs are more affected than other parts of the body, representing 86.9% of injuries. 6Another author had consistent results, noting that 85.5% of the identified injuries affected the same anatomical region. 5The lower limbs are the most required in soccer, explaining the higher frequency of injuries in this area. 80][11] Strain results from fiber stretching beyond the physiological limits.It occurs during extravagant muscle contractions, such as rapid acceleration and deceleration, predisposing the player to an increased injury rate, with excess muscle tone as a major risk factor. 10lthough with a lower incidence, studies also mentioned other injuries, including sprains, contractures, and ligament ruptures.A sprain is a traumatic ligament injury affecting joint ligaments, particularly the ankle.In this injury, the main ligaments involved include the deltoid, anterior talofibular, and posterior talofibular.This type of trauma results from sudden movements, as small, repetitive injuries due to excessive activity can increase ligament fragility.The mechanism of this injury mainly results from plantar flexion during foot inversion, leading to a complete or partial rupture of the lateral ligaments. 12,13Knee sprains are also common in soccer due to valgus torsion, that is, when the knee is directed sharply to the inside and the foot remains fixed.In this case, in addition to ligament lesions, meniscus injuries may occur. 14,15ontracture results from an incorrect muscle contraction with no return to its regular relaxation state.Contractures occur due to lactic acid accumulation from anaerobic respiration after excessive overload. 16Muscles damaged by this injury include the semitendinosus, semimembranosus, and biceps femoris.Soccer players are more susceptible to contractures, especially in the quadriceps, posterior thigh, gastrocnemius, and soleus, mainly from fatigue. 9,16,17,29igament tears depend on the performed movement and mainly affect the anterior and posterior cruciate ligament.Anterior cruciate ligament injury, for instance, is common in athletes due to knee rotation with a fixed foot (facilitated by shoe cleats) and valgus stress in a deceleration movement, abrupt directional change, or both. 18,19This injury can disrupt knee integrity and functionality in the long term and be irreversible; therefore, it accounts for many early retirements of soccer players. 20The anterior talofibular ligament suffers injuries by excessive lateralization when walking on uneven surfaces.

FIFA11þ Prevention Program
The FIFA11þ prevention program had significantly better outcomes than the regular warm-up.As functional capacity influences the risk of injuries, athletes under 15 years old are more susceptible to them because of their lower physical development; as a result, a high physical demand can overload these players. 25IFA11þ considerably reduced injuries in commonly affected areas, including the knee, leg, and ankle.A special reduction occurred in contact, non-contact, and excessive use injuries. 26s for professional players, FIFA11þ led to less impressive outcomes due to the competition calendar, short breaks between matches, and the highly physically demanding routine.However, it improved variables critical for good performance, such as the athlete's dynamic postural control. 27

Final Considerations
The high physical demand influences an increase in the occurrence of muscle and ligament injuries in professional soccer players.Considering functional capacity, the increased intensity in the transition between base and professional categories, and the amount of training and competition calendars of official matches in professional soccer are relevant factors.The lower limbs are the most affected, and the most prevalent injuries include strains, sprains, contractures, and ligament ruptures.
Given the propensity for soccer injuries, it is critical to implement preventive interventions to care for the athletes' health.In this sense, we recommend FIFA 11þ or another customized method developed by the medical department of each club, taking into account individual features.These programs may reduce collective performance losses and health expenses.
Further studies are required to address the effects of the exacerbated routine of professional athletes and improve the performance and physical health of each player to increase the success in preventing injuries.

Financial Support
The authors declare that the present study did not receive financial support from public, commercial, or not-forprofit sources.

Table 1
Articles included in the systematic review